The present invention is directed toward a process and apparatus for the production of nanofibers. Specifically, the nanofibers are produced by a process utilizing pressurized gas, and the apparatus is specifically adapted to deliver fiber-forming material to a pressurized gas stream and thereby initiate the formation of nanofibers.
Nanofiber technology has not yet developed commercially and therefore engineers and entrepreneurs have not had a source of nanofiber to incorporate into their designs. Uses for nanofibers will grow with improved prospects for cost-efficient manufacturing, and development of significant markets for nanofibers is almost certain in the next few years. The leaders in the introduction of nanofibers into useful products are already underway in the high performance filter industry. In the biomaterials area, there is a strong industrial interest in the development of structures to support living cells. The protective clothing and textile applications of nanofibers are of interest to the designers of sports wear, and to the military, since the high surface area per unit mass of nanofibers can provide a fairly comfortable garment with a useful level of protection against chemical and biological warfare agents.
Carbon nanofibers are potentially useful in reinforced composites, as supports for catalysts in high temperature reactions, heat management, reinforcement of elastomers, filters for liquids and gases, and as a component of protective clothing. Nanofibers of carbon or polymer are likely to find applications in reinforced composites, substrates for enzymes and catalysts, applying pesticides to plants, textiles with improved comfort and protection, advanced filters for aerosols or particles with nanometer scale dimensions, aerospace thermal management application, and sensors with fast response times to changes in temperature and chemical environment. Ceramic nanofibers made from polymeric intermediates are likely to be useful as catalyst supports, reinforcing fibers for use at high temperatures, and for the construction of filters for hot, reactive gases and liquids.
It is known to produce nanofibers by using electrospinning techniques. These techniques, however, have been problematic because some spinnable fluids are very viscus and require higher forces than electric fields can supply before sparking occurs, i.e., there is a dielectric breakdown in the air. Likewise, these techniques have been problematic where higher temperatures are required because high temperatures increase the conductivity of structural parts and complicate the control of high electrical fields.
It is known to use pressurized gas to create polymer fibers by using melt-blowing techniques. According to these techniques, a stream of molten polymer is extruded into a jet of gas. These polymer fibers, however, are rather large in that the fibers are greater than 1,000 nanometers in diameter and more typically greater than 10,000 nanofibers in diameter. It is also known to combine electrospinning techniques with melt-blowing techniques. But, the combination of an electric field has not proved to be successful in producing nanofibers inasmuch as an electric field does not produce stretching forces large enough to draw the fibers because the electric fields are limited by the dielectric breakdown strength of air.
Many nozzles and similar apparatus that are used in conjunction with pressurized gas are also known in the art. For example, the art for producing small liquid droplets includes numerous spraying apparatus including those that are used for air brushes or pesticide sprayers. But, there are no apparatus or nozzles capable of producing nanofibers.
It is therefore an object of the present invention to provide a method for forming nanofibers.
It is another object of the present invention to provide a method for forming nanofibers having a diameter less than about 3,000 nanometers.
It is a further object of the present invention to provide an economical and commercially viable method for forming nanofibers.
It is still another object of the present invention to provide a nozzle that, in conjunction with pressurized gas, produces nanofibers.
It is yet another object of the present invention to provide a method for forming nanofibers from fiber-forming polymers.
It is still yet another object of the present invention to provide a method for forming nanofibers from fiber-forming ceramic precursors.
It is still yet another object of the present invention to provide a method for forming nanofibers from fiber-forming carbon precursors.
It is another object of the present invention to provide a method for forming nanofibers by using pressurized gas.
It is another object of the present invention to provide a method for the formation of acicular nanofibers.
It is another object of the present invention to provide a method for the formation of acicular nanofibers having a length up to about 20,000 nanometers, and having a diameter less than about 3000 nanometers.
It is yet another object of the present invention to provide a nozzle that, in conjunction with pressurized gas, produces nanofibers having a diameter less than about 3,000 nanometers.
At least one or more of the foregoing objects, together with the advantages thereof over the known art relating to the manufacture of nanofibers, will become apparent from the specification that follows and are accomplished by the invention as hereinafter described and claimed.
In general the present invention provides a process for forming nanofibers comprising the steps of feeding a fiber-forming material into an annular column, the column having an exit orifice, directing the fiber-forming material into an gas jet space, thereby forming an annular film of fiber-forming material, the annular film having an inner circumference, simultaneously forcing gas through a gas column, which is concentrically positioned within the annular column, and into the gas jet space, thereby causing the gas to contact the inner circumference of the annular film, and ejects the fiber-forming material from the exit orifice of the annular column in the form of a plurality of strands of fiber-forming material that solidify and form nanofibers having a diameter up to about 3,000 nanometers.
The present invention also includes a nozzle for forming nanofibers by using a pressurized gas stream comprising a center tube, a supply tube that is positioned concentrically around and apart from said center tube, wherein said center tube and said supply tube form an annular column, and wherein said center tube is positioned within said supply tube so that an gas jet space is created between a lower end of said center tube and a lower end of said supply tube.